1. Field of the Invention
The present invention relates to cassette loaded cameras of the 35 mm type and more particularly to providing such cameras with means for facilitating the removal and subsequent replacement of cassettes holding partially exposed film.
2. Brief Description of the Prior Art
If a photographer, using a conventional 35 mm camera, removes a partially exposed film cassette to replace it with another cassette containing a different type of film, he encounters a number of problems when he later wishes to expose the rest of the film in the former cassette.
When the photographer rewinds the partially exposed film, he must be certain that the exposed portion is fully received in the cassette to protect it from light, but at the same time he must be careful to leave the leader portion of the film extending out of the cassette so that he can later re-attach it to the film takeup spool in the camera. Some 35 mm cameras with electrically powered rewind mechanisms leave the leader of the rewound film extending out of the cassette, but with most relatively inexpensive 35 mm cameras, the photographer must tactily or audibly sense the separation of the film from the takeup spool, which requires considerable experience and skill.
Assuming that he successfuly performed the rewinding operation, the photographer then opens the camera door to remove the cassette with the partially exposed film. With most cameras, the opening of the door automatically resets the film counter in preparation for the installation of the next cassette. Therefore, if the photographer forgets to observe the counter before opening the door, he can no longer determine how many film frames were exposed and therefore must guess the frame number if he later re-installs the cassette to expose the remaining film. Finally, if he successfully surmounts the foregoing difficulties and reloads the partially exposed cassette in the camera, the photographer now must return the film to the next available exposure frame. This requires him alternately to advance the film and release the shutter with the lens cap in place, until the counter indicates that the film has been advanced to its previous condition.
Previously, various arrangements have been proposed to facilitate the removal and subsequent replacement of a partially exposed strip of film in a camera. For example, U.S. Pat. No. 4,034,393 discloses providing a cassette-loaded filmstrip with a tab that prevents the leader end of the strip from being rewound into the cassette and with a label that serves both to simplify recording the number of exposures previously made on the film and also to facilitate properly re-aligning the film's sprocket holes with the camera's metering mechanism when the film is subsequently re-loaded into the camera. The film counter disclosed in that reference automatically resets when the camera's door is opened, and therefore does not avoid the previously-mentioned problems caused by the failure of the photographer to make a timely notation of the number of exposures that have been made on the partially exposed filmstrip.
Another such arrangement, which is directed entirely to the camera rather than to modifications of the film or its cassette, is disclosed in U.S. Pat. No. 3,511,153. In accordance with this reference, a film counting mechanism always begins its operation with the same tooth of its film metering sprocket in initial engagement with the same sprocket hole of any filmstrip, thus assuring exact registration of exposed frames after reloading of the cartridge. The exposure counter is reset either manually or automatically, but no provision is made for automatically preserving the counter reading when partially exposed film is removed, while also insuring that the counter is reset properly when a new unexposed film cassette is loaded into the camera. It should be noted that although some cameras have counters that must be manually reset and which thereby inherently preserve the last exposure identification, for example the camera shown in U.S. Pat. No. 2,591,417, the advantage that such a counter may afford in removing and subsequently replacing partially exposed film is offset by the likelihood that the photographer will forget to reset the counter when a new film cassette is loaded into the camera. The latter is obviously a much more common occurrence than the removal and subsequent re-loading of partially exposed film.
Another approach to facilitating removal and subsequent re-loading of partially exposed film involves loading the film cassette (or a spool of paper backed roll film) into an auxiliary container or magazine that is removable from the camera without exposing the film to light and that includes its own exposure counter, which preserves its reading whenever the auxiliary container or magazine is removed from the camera. Cameras incorporating this type of construction are shown, for example, in U.S. Pat. Nos. 2,469,008; 2,927,518; 3,006,261; 3,474,714; 3,443,501; and 3,805,277. Cameras of this type indeed minimize the specific problems previously discussed, but this type of camera has not become popular among amateur photographers, presumably because of the expense and bulkiness of the auxiliary film containers or magazines and the resulting increase in the size, weight, and cost of the complete camera.